Methods to adapt air-fuel (a/f) controls for catalyst aging

ABSTRACT

A system includes an exhaust treatment system configured to treat emissions from a combustion engine via a catalyst. The system includes a controller configured to obtain an operating parameter indicating catalyst performance. The controller is configured to determine a deterioration factor indicating deterioration of the catalyst based at least in part on the operating parameter. The controller is configured to determine an adaptation term configured to modify an air-fuel ratio command for the combustion engine to account for the deterioration.

BACKGROUND

The subject matter disclosed herein relates to an exhaust treatmentsystem for an internal combustion engine and, more specifically, toadapting controls based on catalyst performance.

Engines (e.g., internal combustion engines such as reciprocating enginesor gas turbines) combust a mixture of fuel and air to generatecombustion gases that apply a driving force to a component of the engine(e.g., to move a piston or drive a turbine). Subsequently, thecombustion gases exit the engine as an exhaust, which may be subject toexhaust treatment systems that include one or more catalytic converters(e.g., three-way catalyst (TWC) assembly, selective catalytic reduction(SCR) assembly) to reduce the emissions of nitrogen oxides (NO_(X)),hydrocarbons (HC), carbon monoxide (CO), and other emissions. However,the effectiveness of the catalysts at reducing emissions may decreaseover time, resulting in the engine falling out of emissions compliance.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimedsubject matter are summarized below. These embodiments are not intendedto limit the scope of the claimed subject matter, but rather theseembodiments are intended only to provide a brief summary of possibleforms of the subject matter. Indeed, the subject matter may encompass avariety of forms that may be similar to or different from theembodiments set forth below.

In a first embodiment, a system includes an exhaust treatment systemconfigured to treat emissions from a combustion engine via a catalyst,and a controller configured to obtain an operating parameter indicatingcatalyst performance, determine a deterioration factor indicatingdeterioration of the catalyst based at least in part on the operatingparameter, determine an adaptation term configured to modify an air-fuelratio command for the combustion engine to account for the deteriorationfactor of the catalyst, and generate a signal indicating the adaptationterm.

In a second embodiment, an electronic control unit includes a processoroperatively coupled to a memory, wherein the processor is programmed toexecute instructions on the memory to obtain an operating parameter thatindicates how well a catalyst is performing in treating emissions from acombustion engine, determine a deterioration factor that indicates howmuch the catalyst has deteriorated based at least in part on theoperating parameter, determine an adaptation term configured to modifyan air-fuel ratio command for the combustion engine to account for thedeterioration factor of the catalyst, and generate a signal indicatingthe adaptation term.

In a third embodiment, one or more non-transitory computer-readablemedia encoding one or more processor-executable routines wherein the oneor more routines, when executed by a processor of a controller, causeacts to be performed including obtaining an operating parameter thatindicates a conversion performance of a catalyst in treating emissionsfrom a combustion engine, determining a deterioration factor thatindicates how much the catalyst has deteriorated based at least in parton the operating parameter, determining an adaptation term configured tomodify an air-fuel ratio command for the combustion engine to accountfor deterioration factors of the catalyst, and generating a signalindicating of the adaptation term.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present subjectmatter will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic diagram of an embodiment of a three-way catalyst(TWC) exhaust treatment (e.g., aftertreatment) system coupled to anengine;

FIG. 2 is a schematic diagram of an embodiment of the functionaloperation of a controller (e.g., an electronic control unit (ECU)) thatcontrols the air-fuel command of the engine of FIG. 1;

FIG. 3 is a flow diagram of an embodiment of a process performed by aprocessor of the controller of FIG. 1;

FIG. 4 is a schematic diagram of an embodiment of a selective catalyticreduction (SCR) exhaust treatment system for a lean burn engine;

FIG. 5 is a schematic diagram of an embodiment of a function operationof a controller (e.g., an electronic control unit (ECU)) that controlsthe air-fuel command of the lean burn engine of FIG. 4; and

FIG. 6 is a flow diagram of an embodiment of a process performed by aprocessor of the controllers of FIG. 5.

DETAILED DESCRIPTION

One or more specific embodiments of the present subject matter will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the present subjectmatter, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The present disclosure is directed to systems and methods for monitoringor estimating the deterioration of catalysts in catalytic converters andadjusting controls in response to the detected or estimateddeterioration (e.g., deactivation of catalysts). The system and methoddiscussed herein may be performed in three-way catalyst (TWC) and/orselective catalytic reduction (SCR) exhaust treatment systems. Exhausttreatment (e.g., aftertreatment) systems are configured to couple tocombustion engines to treat emissions (e.g., in the engine exhaust) fromthe combustion engine. The exhaust treatment system may include acatalyst based system, such as a TWC system that utilizes a catalyst toconvert harmful pollutants, such as NO_(X), HC, CO, to less toxicemissions. Unfortunately, subjecting the TWC to certain operatingconditions over time often causes changes in the number and type ofactive sites reactions take place on. The loss of active sites on thesurface of the catalysts can result in a loss of conversion performance(i.e., how well the catalyst is operating). As catalyst conversionperformance decreases, the emissions of pollutants (e.g., NO_(X), HC,CO, etc.) from the engine can exceed emission compliance values (e.g.,thresholds or requirements). By adapting the air-fuel ratio controls ofthe engine based on the catalyst performance, the engine can remain inemissions compliance for a longer duration of time than if the air-fuelratio controls were not adapted based on catalyst performance.

The disclosed embodiments include measuring or obtaining one or moreoperating parameters of a combustion engine that indicate the conversionperformance of the catalysts. The operating parameters may include anyactual or estimated aspects of the system performance suitable forindicating the conversion performance of the catalysts, such as time(e.g., engine run time, catalyst aging time, times at different enginetemperatures, etc.), temperatures, flow rates, and/or emissionmeasurements. The conversion performance may describe how well thecatalyst is performing at converting pollutants to less harmfulemissions. A control system may determine a deterioration factor thatindicates how much the catalyst has deteriorated (e.g., over a period oftime) based on the operating parameter. The control system may thenadapt air-fuel controls of the combustion engine based on the conversionperformance to account for deterioration of the catalyst, such as theloss of active sites on the catalyst due to aging, temperature, flowrate, and/or species inputs.

Turning now to the drawings and referring to FIG. 1, a schematic diagramof a TWC exhaust treatment (e.g., aftertreatment) system 6 coupled to anengine 12 is illustrated. As described in detail below, the disclosedexhaust treatment system 6 monitors operating parameters (e.g.,oxidation state) of a catalyst assembly 14 of the exhaust treatmentsystem 6. The engine 12 may include an internal combustion engine suchas a reciprocating engine (e.g., multi-stroke engine such as two-strokeengine, four-stroke engine, six-stroke engine, etc.) or a gas turbineengine. The engine 12 may operate on a variety fuels (e.g., natural gas,diesel, syngas, gasoline, blends of fuel (e.g., methane, propane,ethane, etc.), etc.). The engine 12 may be part of a power generationsystem that generates power ranging from 10 kW to 10 MW. In someembodiments, the engine 12 may operate at less than approximately 1800revolutions per minute (RPM). In some embodiments, the engine 12 mayoperate at less than approximately 2000 RPM, 1900 RPM, 1700 RPM, 1600RPM, 1500 RPM, 1400 RPM, 1300 RPM, 1200 RPM, 1000 RPM, or 900 RPM. Insome embodiments, the engine 12 may operate between approximately800-2000 RPM, 900-1800 RPM, or 1000-1600 RPM. In some embodiments, theengine 12 may operate at approximately 1800 RPM, 1500 RPM, 1200 RPM,1000 RPM, or 900 RPM. Exemplary engines 12 may include General ElectricCompany's Jenbacher Engines (e.g., Jenbacher Type 2, Type 3, Type 4,Type 6 or J920 FleXtra) or Waukesha Engines (e.g., Waukesha VGF, VHP,APG, 275GL), for example.

During operation, the engine 12 receives air 8 (e.g., an oxidant) andfuel 10 that are used in a combustion process to apply a driving forceto a component of the engine 12 (e.g., one or more pistons reciprocatingin cylinders or one more turbines). The combustion gases 16 subsequentlyexit the engine 12 as an exhaust 16, which includes a variety ofemissions (e.g., NO_(X), HC, CO, or other pollutants). The exhausttreatment system 6 treats these emissions to generate milder emissions(carbon dioxide (CO₂), water, etc). As depicted, the exhaust treatmentsystem 6 includes the catalytic converter or catalyst assembly 14. Thecatalyst assembly 14 (e.g., TWC assembly) includes an inlet 18 toreceive the exhaust 16 (e.g., fluid) from the engine 12 and an outlet 20to discharge treated engine exhaust 22. As shown in FIG. 1, the catalystassembly 14 includes a TWC assembly. The TWC assembly, via its catalyticactivity, reduces NO_(X) via multiple reactions. For example, NO_(X) maybe reduced via CO to generate N₂ and CO₂, NO_(X) may be reduced via H₂to generate NH₃, N₂, and water, and NO_(X) may be reduced via ahydrocarbon (e.g., C₃H₆) to generate N₂, CO₂, and water. The TWCassembly also oxidizes CO to CO₂, and oxidizes unburnt HC to CO₂ andwater.

The engine 12 may operate as a rich-burn engine or a lean-burn enginedepending on the mass ratio of air 8 to fuel 10 (AFR). In embodimentsthat include the TWC assembly, the engine 12 may be operated as arich-burn engine (e.g., equivalence ratio (i.e., ratio of actual AFR tostoichiometric AFR), or lambda (λ) value oscillating around 1 (e.g.,stoichiometric engine)) to maximize the catalytic activity in the TWCassembly. In other embodiments, the catalyst assembly 14 may include anyother type of oxidation catalyst (e.g., two-way catalyst, hydrocarbonoxidation catalyst, diesel oxidation catalyst, etc.). In certainembodiments, the exhaust treatment system 6 may include one or moreadditional catalyst assemblies disposed upstream and/or downstream ofthe catalyst assembly 14 (e.g., an ASC assembly disposed between theengine 12 and the catalyst assembly). In certain embodiments, theexhaust treatment system 6 may include other components (e.g., anoxidant injection system that injects air 8 (e.g., an oxidant, O₂,O₂-enriched air, or O₂-reduced air) into the exhaust 16).

The engine 12 and the exhaust treatment system 6 are coupled (e.g.,communicatively) to a controller 24 (e.g., an engine control unit (ECU))that controls and monitors the various operations of the engine 12. Thecontroller 24 may include multiple controllers in communication witheach other (e.g., a respective controller for the engine 12 and theexhaust treatment system 6). The controller 24 includes processingcircuitry (e.g., processor 26) and memory circuitry (e.g., memory 28).The processor 26 may include multiple microprocessors, one or more“general-purpose” microprocessors, one or more special-purposemicroprocessors, and/or one or more application specific integratedcircuits (ASICS), system-on-chip (SoC) device, or some other processorconfiguration. For example, the processor 26 may include one or morereduced instruction set (RISC) processors or complex instruction set(CISC) processors. The processor 26 may execute instructions to carryout the operation of the engine 12 and/or exhaust treatment system 6.These instructions may be encoded in programs or code stored in atangible non-transitory computer-readable medium (e.g., an optical disc,solid state device, chip, firmware, etc.) such as the memory 28. Incertain embodiments, the memory 28 may be wholly or partially removablefrom the controller 24.

The memory 28 may store various tables (e.g., look-up tables (LUT)). Thememory 28 may also store models (e.g., software models representingand/or simulating various aspects of the engine 12, the exhausttreatment system 6, and/or each of their components). For example, thememory 28 may store models used to estimate how flow rate, temperature,oxygen, or emissions correspond to catalyst performance. The models maybe used to compare estimated values to measured values indicating theconversion performance of the catalyst.

The processor 26 of the controller 24 may be configured to executeinstructions to control various aspects of the engine, such as theair-fuel ratio (AFR). That is, the processor 26 may be configured tocontrol air 8 and fuel 10 quantities that enter the engine 12 during thecombustion process to optimize the performance of the engine 12 (e.g.,based on throttle, output, RPM, or any number of factors). Further, thecontroller 24 also controls and/or monitors the operations of theexhaust treatment system 6, such as the AFR. In an embodiment, theprocessor 26 may control the air 8 and fuel 10 quantities based at leastin part on an adaptation term (e.g., part, aspect, etc.) that accountsfor changes (e.g., deterioration) in the conversion performance of thecatalyst.

FIG. 2 is a schematic diagram of functional operations 40 for thecontroller 24 to control the AFR of the engine 12 of FIG. 1. All or someof the steps of the functional operations 40 described in FIG. 2 may beexecuted by the controller 24 (e.g., utilizing the processor 26 toexecute programs and access data stored on the memory 28). In addition,one or more of these steps may be performed simultaneously with othersteps.

The operations 40 of FIG. 2 may be performed to adapt an AFR command 38to account for decreasing conversion performance of the catalyst. Theconversion performance may deteriorate as the number of active sitesthat reactions take place on decrease. The loss of active sites (i.e.,the loss of conversion performance) may occur due to aging, flow rate,temperature, and/or species inputs. The processor 26 may determine anadaptation term to account for the deterioration of the catalyst. Theadaptation term is configured to modify the air-fuel ratio command 38 ofthe combustion engine 12 based at least in part on the conversionperformance.

To account for aging of the catalyst, a clock 42 may be utilized toprovide an amount of time 42 (e.g., how long the catalyst has beenoperating) based on clock cycles for the processor 26 to access. Theprocessor 26 may utilize one or more look up tables (LUT) stored the inmemory 28, such as an omega parameter LUT 44 and/or a NO_(X), CO, orpost catalyst emission LUT 46. The omega parameter LUT 44 may includeone or more catalysts, such as a platinum group metal (PGM), ceria, orany other suitable catalyst and an omega parameter that indicates howthe catalyst ages over time. As such, the omega parameter LUT 44 mayprovide a deterioration factor 48 (e.g., Omega_PGM, Omega_Ceria, etc.)that indicates how much the catalyst has deteriorated (e.g., due toaging) based at least in part on one or more operating parameters, suchas the time (e.g., from clock 42) and/or a type of the catalyst (e.g.,PGM, Ceria, etc.), as different catalysts may age at different rates.The processor 26 may adjust the deterioration factor 48 linearly and/orexponentially, as the deterioration of some types of catalysts may varylinearly and/or exponentially based on time. The deterioration factor 48may also be based on precious metal loading of the catalyst.

The deterioration factor 48 may further account for other causes oflosses in conversion performance in the catalyst, such as flow rate,temperature, and species inputs. The various sensors 34 coupled to thesystem 6 may detect operating parameters that may be suitable forestablishing deterioration factors. For example, temperature may bedetected via the sensors 34. As high temperatures may cause a decreasein conversion performance, the processor 26 may utilize the model basedestimator 50 to determine a deterioration factor 48 that accounts fortemperature. For example, the model may have temperatures thatcorrespond to different rates of aging of the catalyst. As a furtherexample, the model based estimator 50 may use a measured oxygen value(e.g., how much oxygen is missing from the expected amounts of O₂storage 60) when determining deterioration factors. The model may begeneral to any type of catalyst or specific to certain catalysts. Asmentioned above, the processor 26 may account for changes in catalystconversion performance by varying the deterioration factor 48 linearlyand/or exponentially proportional to precious metal loading.

The controller 24 may use a model stored in the memory to estimate theemissions of certain species (e.g., NO_(X) and NH₃). The processor 26may utilize a NO_(X), CO, or post catalyst emission LUT 46 to determinethe deterioration factors 52 based at least in part on pre or postcatalyst emission values. That is, based on the amounts of variousemissions, the processor 26 may determine a deterioration factor 52 forhow well the catalyst is performing. The deterioration factor 52 basedon emissions may then be compared to the O₂ storage data. In theembodiment shown in FIG. 2, the species control 58 can modify the O₂storage set-point given the oxygen storage control 60. Alternativelyand/or additionally, the O₂ storage control 60 set-point may be used tomodify the species control 62.

The processor 26 may determine the adaptation term 64 to modify theair-fuel ratio command 38 provided to the combustion engine to accountfor the one or more deterioration factors 48, 52 of the catalyst. Thecontroller 24 may then regulate or adjust the air-fuel ratio of theengine 12 based on the air-fuel ratio command 38. Additionally and/oralternatively, the controller 24 may control one or more other engineoperating parameters, such as spark timing. By modifying the air-fuelratio command 38, the controller 24 can allow the engine 12 to remain inemissions compliance for an extended duration of time longer as thecatalyst ages, where the extended duration of time is longer than aduration of time had the air-fuel ratio not been modified. By extendingthe duration of remaining in compliance, the controller 24 reducesmaintenance and further improving operation of the engine. Theadaptation term 64 may include a linear or weighted combination ofoxygen storage control 60 estimates and/or species concentrationestimates. As explained above, the oxygen storage estimates and/orspecies concentration estimates utilize maps (e.g., LUT 44, 46) ofdeterioration factors to analyze the operating parameters.

The processor 26 may execute instructions (e.g., code) stored on thememory 28 to carry out the operation of the engine 12 and/or exhausttreatment system 6 in accordance with the processes described herein.FIG. 3 is a flow diagram of an embodiment of a process 64 performed byone or more of the processors 26 of the controller 24. This process 64may be applied to TWC catalyst systems. The process 64 may begin byobtaining signals indicating catalyst performance (block 66). Catalystperformance indications may be obtained via the sensors 34, 36 and/orthe clock 42. The process 64 may then continue by determining (block 68)a deterioration factor indicating how much the catalyst has deterioratedbased on the catalyst performance. Next, one or more of the processors26 may determine an adaptation term to modify the air-fuel ratio of theengine to account for the deterioration factor (block 70). Then, theprocessor 26 may generate a signal that is based on the adaptation termthat modifies the air-fuel ratio. For example, the processor 26 maygenerate a signal indicating the adaptation term (block 72). Theprocessor 26 may then modify the air-fuel ratio of the combustion enginebased on the adaptation term (block 74). By modifying the air-fuel ratiocommand or the oxidant injection based on an adaptation term thataccounts for aging of a catalyst, the controller can enable thecombustion engine to remain in emissions compliance for an extendedduration of time as the catalyst ages.

The systems and methods may be applied to selective catalytic reduction(SCR) exhaust treatment systems for lean-burn engine exhaust treatmentcontrols. FIG. 4 is schematic diagram of an embodiment of an SCR exhausttreatment system 78 that uses an SCR catalyst assembly 80 for alean-burn engine 82. Similar to the TWC system described with respect toFIG. 1, the lean-burn engine 82 is coupled to a controller (e.g., enginecontrol unit) 84 that controls and monitors the operations of the engine82. The engine controller 84 includes processing circuitry (e.g.,processor 86) and memory circuitry (e.g., memory 88). The processor 86may execute instructions (e.g., stored in the memory 88) to carry outthe operation of the engine 82. The processor 86 of the controller 84may operate similar to the controller 24 and may be configured togenerate one or more commands to control the engine 82, such as areductant injection (e.g., anhydrous ammonia, aqueous ammonia, or urea)command 90 that controls the reductant that injected the engine 82.

The SCR exhaust treatment system 78 may convert pollutants, such asNO_(X) emissions, from the exhaust 92 of the engine 82. Further, the SCRexhaust treatment system 78 may include a reductant injection system 94that injects a reductant, such as NH₃ or urea, into the exhaust 92 andreceived by the SCR catalyst assembly 80. The lean-burn engine 82 maygenerate exhaust 92 having NO_(X) or other undesirable pollutants whichare output at various temperatures and flow rates. Sensors 96 arecoupled to or downstream of the engine 82 and are configured to measurethe temperature and flow rates of the various exhaust 92 parameters. Forexample, the sensors 96 may include one or more pre-SCR ammonia (NH₃)sensors 98 and/or one or more pre-SCR nitrogen oxides (NO_(x)) sensors100 configured to measure the concentrations of the the reductant and/orthe pollutants, respectively, in the exhaust 92. Further, one or morepost-SCR NH₃ sensors 102 and/or NO_(X) sensors 106 may be disposeddownstream of the catalyst assembly to measure a concentration or anamount of pollutants and/or reductants in the treated engine exhaust101. Even further, one or more RF probes or sensors 108 may be disposedwithin or coupled to the catalyst assembly 80 to measure reductantstorage of the catalyst assembly 80. In certain embodiments, the NH₃storage measurement from the RF probes 108 may take the form of avoltage reading. In certain embodiments, the voltage reading may beconverted to an NH₃ storage value, θ (e.g., utilizing a LUT).

Signals from the sensors 96, 102, 108 may be used by a reductioninjection controller 112. The reduction injection controller 112 mayinclude a processor 114 and/or a memory 116. The processor 114 and thememory 116 may be used to execute instructions related to controllingthe reductant injected into the exhaust 92. Additionally, signals may besent to the engine controller 84 for the engine controller 84 to controloperating parameters of the engine based on reductant measurements.

The controllers 84 and/or 112 may modify the reductant injection basedon catalytic performance to allow the lean-burn engine 82 to remain incompliance for an extended period of time. That is, the controllers 84and/or 112 enable the engine to be in emissions compliance for a periodof time longer than if the controllers 84 and/or 112 did not modify thereductant injection based on the catalytic performance. FIG. 5 is aschematic diagram of function operations for the controllers 84 and/or112 to adapt the reductant injection to the exhaust of the engine 82based on the catalytic performance. All or some of the steps of thefunctional operations 118 described in FIG. 5 may be executed by thecontrollers 84 and/or 112 (e.g., utilizing the processor 86 to executeprograms and access data stored on the memory 28). In addition, one ormore of these steps may be performed simultaneously with other steps.

Similar to the TWC system described above, these instructions may beencoded in programs or code stored in a tangible non-transitorycomputer-readable medium (e.g., an optical disc, solid state device,chip, firmware, etc.) such as the memory 88. In certain embodiments, thememory 88 may be wholly or partially removable from the controller 24.The memory 88 may store various tables (e.g., look-up tables (LUT)). Thememory 88 may also store models (e.g., software models representingand/or simulating various aspects of the engine 82, the exhausttreatment system 78, and/or each of their components). For example, thememory 88 may store models used to estimate how flow rate, temperature,ammonia, or emissions correspond to catalyst performance. The models maybe used to compare estimated values to measured values indicating theconversion performance of the catalyst.

As catalysts deteriorate over time, the catalysts in the SCR catalystassembly 80 may not convert the pollutants as efficiently and/or reducepollutants enough for the engine 82 to stay in compliance and/or tominimize maintenance. That is, the conversion performance maydeteriorate as the number of active sites that reactions take place ondecrease. The loss of active sites (i.e., the loss of conversionperformance) may occur due to aging, flow rate, temperature, and/orspecies inputs.

The controllers 84 and/or 112 may utilize one or more engine operatingparameters (e.g. actual operating parameters measured by the sensors 96,102, 108 and/or estimated operating parameters), such as the measuredNH₃ and/or NO_(X) concentrations (e.g., received from the NH₃ sensors98, 104 and/or the NO_(X) sensors 100, 106) upstream and downstream ofthe catalyst assembly 80.

The controllers 84 and/or 112 may utilize the signals from the sensors96, 102, 108 to determine a deterioration factor 122 indicating thedeterioration (e.g., due to aging) of the catalyst based on one or moreoperating parameters of catalytic performance, such as a type ofcatalyst, as different catalysts may age at different rates.Alternatively and/or additionally, the processors 86 and/or 114 mayreceive signals from a clock 120 that can be used to estimate thedeterioration of the catalyst. For example, the processors 86 and/or 114may utilize one or more LUTs 124, 126 with times from the clock 120(e.g., based on clock cycles of the processor 86) associated with agingof the catalyst to determine the deterioration factor 122. As timemeasured by the clock 120 progresses, the LUT may provide increasingdeterioration of the catalyst. The processors 86 and/or 114 may adjustthe deterioration factor 122 linearly and/or exponentially, as thedeterioration of some types of catalysts may vary linearly and/orexponentially based on time.

The deterioration factor 122 may further account for other causes oflosses in conversion performance in the catalyst and be used by a modelbased estimator 128 to determine an NH₃ storage control estimationsignal 132. The controller 84 may input the operating parameters and/orthe deterioration factor 122 into the model based estimator 128 (e.g.,software-based model) to generate an estimate of the NH₃ storage control140 state of the catalyst assembly 80 and/or estimates of emissionscontrols 148 for emissions (e.g., NO_(X)) exiting the catalyst assembly80. For example, the measured NH₃ concentration upstream and downstreamof the catalyst assembly 80 may be utilized in the model to generate theestimated NH₃ storage control 140 of the catalyst assembly 80 and/or theestimated NH₃ emissions exiting the catalyst assembly 80. In otherembodiments, the measured NO_(X) concentration upstream and downstreamof the catalyst assembly 80 may be utilized in the model to generate theestimated emissions control for the catalyst assembly 80. The controller84 may compare an estimated NH₃ storage to a measured NH₃ storage (e.g.,based on feedback from the RF probes 108) for the catalyst assembly 80.For example, the model based estimator 128 may determine an estimationsignal 132 that accounts for aging of the catalyst (e.g., via thedeterioration factor 122 from the LUT 124 and/or the LUT 126),temperature, flow rate, and/or species inputs. As explained above withrespect to the TWC catalyst assembly, the model 128 may havetemperatures that correspond to different rates of aging of thecatalyst.

To account for aging of the catalyst, the clock 120 may be utilized toprovide an amount of time (e.g., how long the catalyst has beenoperating) based on clock cycles for the processor 86 and/or 114 toaccess. The processor 86 and/or 114 may utilize the LUT 124 and/or theLUT 126 stored in the memory 88 and/or 116, such as an omega parameterLUT 124 and/or a NH₃, NO_(X), and/or post catalyst emission LUT 126. Theomega parameter LUT 124 may provide a deterioration factor 122 (e.g.,Omega_Vanadium, Omega_zeolite, etc.) that indicates how much thecatalyst has deteriorated (e.g., due to aging) based at least in part onone or more operating parameters, such as the time (e.g., from clock120) and/or a type of the catalyst (e.g., vanadium, zeolite, etc.), asdifferent catalysts may age at different rates. In other words, theprocessor 86 and/or 114 may utilize the LUT 124 and/or post catalystemission LUT 126 to provide omega values based on time and/or a type ofcatalytic components. For example, the omega values may be associatedwith active site density of vanadium, zeolites, and/or precious metals.For instance, as vanadium often does not withstand temperatures as highas zeolite, the processor 86 and/or 114 may determine that vanadiumomega values increase faster than zeolite omega values at highertemperatures than optimal temperatures for vanadium over a similarduration of time. Further, the processor 86 and/or 114 may adjust thedeterioration factor 122 linearly and/or exponentially, as thedeterioration of some types of catalysts may vary linearly and/orexponentially based on time. The deterioration factor 122 may also bebased on precious metal loading of the catalyst.

A similar process may be performed by the processor 86 and/or 114 basedon post catalyst NH₃ and/or NO_(X) emissions. For example, the processor86 and/or 114 may determine the deterioration factor 122 that indicateshow much the catalyst has deteriorated based on NH₃, NO_(X), and/orother post catalyst emissions. The LUT 126 may include differentdeterioration rates based on quantities of NH₃ and/or NO_(X) detected.Further, the deterioration rates may vary depending on the type of postcatalyst emissions, similar to the types of catalysts described above.

The processor 86 may adapt the NH₃ storage 140 of the catalyst assembly80 based on the estimation signal 132 to account for the deteriorationof the catalyst. The estimated variables are then utilized to add anadaptation term 142 to modify the reductant injection command 90 (e.g.,a urea injection command, NH3 injection command, etc.) of the combustionengine 82 based at least in part on the conversion performance.

As shown in FIG. 5, the clock 120 may be used with pre-SCR NH₃ and/orNO_(X), post-catalyst NH₃ and/or NO_(X), or both. That is, thedeterioration factor 122 may be generated from a pre-SCR LUT 124, apost-catalyst LUT 126, or both. In FIG. 5, the estimation signal 132accounts for the deterioration factor 122 using in both pre-SCR (e.g.,reference number 144) and post-catalyst (e.g., reference number 146)values. Further, post catalyst emissions controls 148 may also accountfor the deterioration factor 122 and the reductant injection command 90may be based at least in part on the adaptation terms 142 (e.g., alinear or weighted combination of the one or more adaptation terms 142).

The processor 86 and/or 114 may execute instructions (e.g., code) storedin the memory 88 and/or 116 to carry out the operation of the exhausttreatment system 78 in accordance with the processes described herein.FIG. 6 is a flow diagram of an embodiment of a process 160 performed byone or more of the processors 86 and/or 114 of the engine controller 84and/or the reductant injection controller 112. This process 160 may beapplied to SCR catalysts for lean burn engines. The process 160 maybegin by the processor 86 obtaining signals indicating catalystperformance (block 162). Catalyst performance indications may beobtained via the sensors 96 and/or the clock 120. The process 160 maythen continue by determining (block 164) a deterioration factorindicating how much the catalyst has deteriorated based on the catalystperformance. Next, one or more of the processors 86 and/or 114 maydetermine an adaptation term to modify a reductant injection command forthe engine 82 to account for deterioration of the catalyst (block 166).Then, the processor 86 and/or 114 may generate a signal that is based onthe adaptation term that modifies the reductant injection command. Forexample, the processor 86 and/or 114 may generate a signal indicatingthe reductant injection command (block 166). The processor 86 and/or 114may then modify injection of a reductant based on the reductantinjection command (block 170). By modifying the reductant injectionbased on an adaptation term that accounts for aging of a catalyst, thecontroller can enable the combustion engine 82 to remain in emissionscompliance for an extended duration of time as the catalyst ages.

Technical effects of the present embodiments relate to controlling anair/fuel ratio or reductant injection of an engine. In certainembodiments, the engine may include one or more operating parametersthat are used to indicate catalyst performance. A controller may receivethe operating parameters which may be used to determine a deteriorationfactor of the catalyst. In an embodiment, the deterioration factorindicates aging of the catalyst. The controller may determine anadaptation term to modify an air-fuel ratio or a reductant injection toaccount for the aging of the catalyst. By changing the air-fuel ratio orthe reductant injection, the engine can remain in emissions compliancefor an extended duration and the lifetime of the engine can be improved.

This written description uses examples to disclose the subject matter,including the best mode, and also to enable any person skilled in theart to practice the subject matter, including making and using anydevices or systems and performing any incorporated methods. Thepatentable scope of the subject matter is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

1. A system, comprising: an exhaust treatment system configured to treatemissions from a combustion engine via a catalyst; and a controllerconfigured to: obtain an operating parameter indicating catalystperformance; determine a deterioration factor indicating deteriorationof the catalyst based at least in part on the operating parameter;determine an adaptation term configured to modify an air-fuel ratiocommand for the combustion engine to account for the deteriorationfactor of the catalyst; and generate a signal indicating the adaptationterm.
 2. The system of claim 1, wherein the adaptation term comprises alinear or weighted combination of oxygen storage estimates, speciesconcentration estimates, or any combination thereof.
 3. The system ofclaim 2, wherein the oxygen storage estimates, species concentrationestimates, or any combination thereof, utilize a map of deteriorationfactors to analyze the operating parameter.
 4. The system of claim 1,wherein the controller is configured to modify the air-fuel ratiocommand to enable the combustion engine to be in emissions compliancefor an extended duration of time as the catalyst ages.
 5. The system ofclaim 1, wherein the exhaust treatment system comprises a three-waycatalyst (TWC) assembly.
 6. The system of claim 1, wherein the operatingparameter comprises an indication of time that corresponds to how longthe catalyst has been operating.
 7. The system of claim 1, comprisingthe combustion engine controlled by the controller, and wherein thecontroller regulates or adjusts an air-fuel ratio of the combustionengine based on the air-fuel ratio command.
 8. An electronic controlunit, comprising: a processor operatively coupled to a memory, whereinthe processor is programmed to execute instructions on the memory to:obtain an operating parameter that indicates how well a catalyst isperforming in treating emissions from a combustion engine; determine adeterioration factor that indicates how much the catalyst hasdeteriorated based at least in part on the operating parameter;determine an adaptation term configured to modify an air-fuel ratiocommand for the combustion engine to account for the deteriorationfactor of the catalyst; and generate a signal indicating the adaptationterm.
 9. The electronic control unit of claim 8, wherein the processoris configured to utilize a look-up table that provides omega valuesbased on time and a type of the catalyst, wherein the omega valuesindicate the deterioration factor of the catalyst.
 10. The electroniccontrol unit of claim 9, wherein the omega values are associated withplatinum group metals (PGM), ceria, or any combination thereof.
 11. Theelectronic control unit of claim 9, wherein the omega values are basedon precious metal loading of the catalyst.
 12. The electronic controlunit of claim 8, wherein the deterioration factor of the catalyst islinearly or exponentially adjusted based on time.
 13. The electroniccontrol unit of claim 8, wherein the adaptation term is based at leastin part on a model based estimator that utilizes an amount of oxygen.14. The electronic control unit of claim 8, wherein the adaptation termis based at least in part on flow rate, temperature, species inputs, ora combination thereof.
 15. One or more non-transitory computer-readablemedia encoding one or more processor-executable routines wherein the oneor more routines, when executed by a processor of a controller, causeacts to be performed comprising: obtaining an operating parameter thatindicates a conversion performance of a catalyst in treating emissionsfrom a combustion engine; determining a deterioration factor thatindicates how much the catalyst has deteriorated based at least in parton the operating parameter; determining an adaptation term configured tomodify an air-fuel ratio command for the combustion engine to accountfor deterioration factors of the catalyst; and generating a signalindicating the adaptation term.
 16. The non-transitory computer readablemedium of claim 15, wherein the processor of the controller causes actsto be performed comprising determining the deterioration factor based onmaps of deterioration factors of the catalyst, wherein the maps compriseestimates of oxygen storage, species concentration, or any combinationthereof.
 17. The non-transitory computer readable medium of claim 16,wherein the processor of the controller causes acts to be performedcomprising determining the adaptation term based on the oxygen storage,species concentration estimates, or any combination thereof.
 18. Thenon-transitory computer readable medium of claim 15, wherein determiningthe adaptation term comprises utilizing a look-up table having a map ofdeterioration factors for post-catalyst emissions.
 19. Thenon-transitory computer readable medium of claim 18, wherein the postcatalyst emissions comprise NO_(X), CO, or any combination thereof. 20.The non-transitory computer readable medium of claim 15, wherein the ageof the catalyst is determined based on clock cycles.